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A209049
Smallest pentagonal number with n prime factors (counted with multiplicity).
2
1, 5, 22, 12, 210, 176, 1520, 1080, 8400, 55200, 273280, 43776, 2624832, 7173360, 71660160, 100659200, 34255872, 178962432, 3623854080, 17895751680, 5413478400, 43690752000, 927712542720, 733008101376, 1789570252800, 35917382287360, 50649120571392
OFFSET
0,2
COMMENTS
Pentagonal analogy of A075088.
MATHEMATICA
k = 1; t = Table[0, {50}]; While[k < 500000001, a = PrimeOmega[k] + PrimeOmega[3 k - 1] - 1; If[ t[[a + 1]] == 0, t[[a + 1]] = k; Print[{k, a}]]; k++]; # (3 # - 1)/2 & /@ t
Join[{1}, Table[SelectFirst[{#, PrimeOmega[#]}&/@PolygonalNumber[5, Range[ 110000]], #[[2]]==n&], {n, 20}][[All, 1]]] (* The program generates the first 21 terms of the sequence. *) (* Harvey P. Dale, Dec 27 2022 *)
CROSSREFS
Sequence in context: A247937 A343840 A270406 * A217444 A063619 A229801
KEYWORD
nonn
AUTHOR
Robert G. Wilson v, Mar 04 2012
STATUS
approved